The present invention relates to aircraft flight controls, and more particularly to aircraft flight control laws.
Some helicopters are tasked with performing missions involving the lifting of heavy external loads. Often, these heavy loads are suspended from a helicopter via a hook and cable assembly. In the past, there have been efforts to analyze the external loads and characterize their impact on helicopter handling qualities and dynamic stability margins. One method of compensating for external loads utilizes cable angle feedback, i.e., monitoring the angle of the cable holding the external load in relation to the centerline of the aircraft, to determine the dynamics of the load and then compensates the helicopter based on the mission. Direct feedback of the external load can be used in a similar manner. Unfortunately, these systems require mechanical and electronic measurement devices. Further, if the aircraft control systems track inputs via high gain feedback to improve aircraft handling, then these systems can enter a state of excitation causing an increasing oscillation in the suspended load. This risk of oscillations increases as the discrepancy between pilot or autopilot input and actual aircraft performance increases.
Consequently, there is a need for a system that increases helicopter control and stability without the additional risk of inducing oscillations in the suspended load cable.